Entity - How do I teach a horse to bow?

IV (age of horse) - What exact steps should I take?
What should be my 'bow' cue?
What treats and equipment should I use?
What is the best area to do this in?
How long should I spend on this in each training session?

DV (How long it takes for horse to bow on cue) - What measurements should I use for qualitative?
Are there other measures for quantitative besides time?

Connections - Has age already been correlated with trainability?

proposal